Below the kingdom in the classification system is the phylum. Although there is also a subkingdom / domain classification between 'kingdom' and 'phylum', it is not usually used in biological identification.

Basically, the classification of life is more complex than previously thought (when these terms came into usage). Lord Brawl tells me that Monera has been split up into two kingdoms. I haven't heard, but if it's true, I'll update this, of course. In any case, it's bound to happen sometime. Archaea and Bacteria are more different than plants and animals.

You enter the kingdomWhen the throneIs indistinguishable
From a commoner's comfortable armchairEmanation of the his force of grasp
Extend to the river beyond the canyonWhere tranquil stream and furious billow converge
Into a point of ordered confusion
To be settled by the maidWho stand firmly despite the facade of frailty
With her eyes blindfolded